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Re: Tight gudgeon pins

John Mason
Thank you all for the advice. I am going to go down the route of doing nothing as I now realise that once the engine has warmed through they will be loose. I think normal careful running in once the engine is up and running will free them up.


John Mason


Yup!

Location: Bonnie Galloway

Re: Tight gudgeon pins

John, I would say that if they become easily movable when heated as you describe, I would leave them as they are, making sure that there is a thin film of oil on the pin and the bore in the piston.
Attempting to ream the pistons might cause irepairable damage unless done by a good machine shop.
Awaiting return fire!

Location: Bonnie Galloway

Re: Tight gudgeon pins

personally i dont see the point of boiling the rods and pistons, if these are standard items.

i sometimes find new pistons ive fitted can be tight when fitting from the packet as there is such a fine fitting tolerance,

i find it best to oil the pin, and slide it in and out of the piston until it frees up.

if it was me id remove the tight pins and try this.

you only get one change to do the job right.

if its not, then it will probably be expensive second time round.

tony.

out of interest what pistons are you useing.

Location: huncote on the pig

Re: Tight gudgeon pins

tony betts
personally i dont see the point of boiling the rods and pistons, if these are standard items.

i sometimes find new pistons ive fitted can be tight when fitting from the packet as there is such a fine fitting tolerance,

i find it best to oil the pin, and slide it in and out of the piston until it frees up.

if it was me id remove the tight pins and try this.

you only get one change to do the job right.

if its not, then it will probably be expensive second time round.

tony.

out of interest what pistons are you useing.


Pistons purchased from the Seven Workshop. I am unsure of the make but the pistons came without the rings fitted ( this was no problem however)

John Mason

Re: Tight gudgeon pins

hi john,

its been a wile since ive stocked workshop pistons.

and used to use them when i was building engines for people.

but when i did, they were very good pistons, i find again i had to oil the pin and get it moving in the piston before fitting.

pistons always come without rings fitted.

i always had to gap the rings for these pistons before fitting.

hope this helps tony

Location: huncote on the pig

Re: Tight gudgeon pins

Hi Dave,
Put your tin hat on and take cover!!!
Is not the whole point of a reamer to achieve an engineered finish of the correct diameter? Back in the dark ages when I was an apprentice we were taught that, where applicable, all holes were drilled under size and then hand reamed to fit, especially on air frames where even holes for bolts had to be reamed first!
John has told us that he has had to heat the piston, and con-rod in boiling water, but no mention of heating the gudgeon pin as well.
"When hot the gudgeon pins went in no trouble and everything was free" well yes it would do, but if the pin is heated to the same temperature, would he not be back in the same situation. Tight gudgeon pins are not a good idea. In my "Little box of horrors" I have gudgeon pins with bright blue ends!
Imagine you had just re-bored the block and two of the pistons went in easily but the other two needed, in John's words "Much more effort" No I don't think I'd be happy either.
Just a thought on a cold Sunday afternoon.
J

Location: As far east in Kent as you can get

Re: Tight gudgeon pins

tony betts
its been a wile since ive stocked workshop pistons.

and used to use them when i was building engines for people.

but when i did, they were very good pistons, i find again i had to oil the pin and get it moving in the piston before fitting.


I fit many 7 W/S pistons every year - like you Tony I have found they are very good, if not excellent, pistons and have yet to give me any problems whatsoever.

I always ream the gudgeon pin hole in the rod so that the pin slides in easily and won't damage the piston on assembly.

I don't heat the pistons before assembly as the pins have always slid in easily without the need to.

I always oil the gudgeon pins before assembly, then squirt more in once on the rod, waggle them about like mad, slide them from side to side so as to get it everywhere.

Jobs a good-un.

Re: Tight gudgeon pins

I'll put my tin hat on as well.

As Bob culver suggests with a tolerance of 0.0001 Pistons shouldn't be reamed.

But we don't all have the corect grinding machines for the job.

If you do ream them you at least need to use a 12 cutting edge reamer.

A 6 edge is not accurate enough.

Tony

Location: HUNCOTE on the pig

Re: Tight gudgeon pins

Just a further update. I keep oiling everything and moving them side to side and back and forward. They are becoming a lot better and much more free soon they will be like the other two.

John Mason

Re: Tight gudgeon pins

Re: Tight gudgeon pins

Sounds as though a bit of burnishing was all that was needed.
Good news.

Tony.

Location: Malvern, Melbourne, Australia.

Re: Tight gudgeon pins

This is all good stuff except the reaming bit, I wouldn't do it in any circumstance. Gudgeon pin Bosses are micro-finished and the burnishing referred to by Tony is virtually what I suggested in my 2014 post. I have since used Diesel fuel instead of Kerosine, it is less abrasive than kero. I use a Ryobi Battery drill in low gear to drive the pin via a long 3/16 bolt thru the gudgeon bore, immerse the piston in a bath whilst reciprocating and spinning the pin slowly-works a treat.
Readers will be interested to know that the Rings supplied with Seven Workshop (taiwanese)pistons are manufactured here in Christchurch, New Zealand- a truley international product! They are manufactured with the equipment used here in the 1950s at Presco Piston ring company in Wellington. The company was owned by Charlie Maxwell a keen Vintage motorist and founder member of the Vintage car club of NZ . I also lap the rings to the mating bore with Brasso polish then wash the piston/ring assy in petrol before assembling. this takes the high spots off the rings and assures good compression from day one. Charlie Maxwell advised me to do this. I don't gap the rings before doing this the lapping usually brings the gap right.
Yes they are very good pistons-a copy of Hepolites made by Hepworth and Grandage of Bradford Yorks.I have ,like R never have- had a problem with them.
Cheers Steve H

Location: Wellington New Zealand

Re: Tight gudgeon pins

Hi Steve

That went in a mighty circle but at least the hazards of trying to ream pistons have been emphasised!

I have always been annoyed by rough turned rings, esp when gap recommended at .003 per inch. I suspect after 10 miles the gaps are beyond max fitting tolerance. If pregapped often large to start with. Usually with Sevens enough old blocks to use as laps.

ACL and American hot rod books make much of removing honing debris. They reckon petrol n.b.g. Recommend soap, followed by thin oil swabs, and insist OK only when no darkness on a white cloth.

Location: Auckland, NZ