Advice on measuring squish

[djh66]

clutching at straws here but you ve not got the piston for a tv175 crank on a 107 rod have you? what casings?

LiS 150 casings, standard gp MEC race crank, complete gt 186 kit inc. head & AOKI piston to suit RD350LC/ YPVS/ RD400 64mm all from Gran Sport.

Is it possible the piston is for the longer tv crank?

[Bufficus]

heres a question for those in the know!
if the above example is 1.2mm why does a solder squish test show 1.4mm but the actual squish is 1mm and tighter ???????????

(Not in the know)
Dwell?

[Darrell Taylor]

not dwell

[drunkmunkey6969]

Although the measured areas (deck height, gasket thicknes, cyl head rebate) are fixed values....the bearings (little end, big end, main shaft etc) piston and rod all have clearance values which might show up when compressing a solid within the crown. However as the engine heats up, metals expand (bearings, piston crowns etc) and reduce clearances, plus rods and such can stretch at high rpm further reducing clearances....which means pistons can kiss the head at extreme revs/temps if clearances are insufficient. Further down the line, when heads are re-torqued n such, gaskets can also compress further.

Sent from my HTC Sensation using Tapatalk

[djh66]

When I assembled it with no gaskets, I still had a squish of +3mm. In fact the piston at TDC is about 3mm below the barrel line (when veiwing with no head on). Something isn't right! Surely on a new kit, I should need to get the barrel and head re machined??

[drunkmunkey6969]

Sounds like wrong piston for the rod...

Sent from my HTC Sensation using Tapatalk

[Darrell Taylor]

thats about correct Dan , wow 4.46 am sounds like u had a good night out

this is how it can be put to good use
i use the method to check wear on race motors thru the season
start with 1.2 squish with solder and 1.1mm without shows a 0.1 deflection down due to tolerances in bearings which will mean on the up stroke with extension of components will reult in a 1mm squish thats without heat expansion and rod stretch etc ,i find towards the end of the season the squish gets bigger ,too big is followed by a bearing failure
the narrow nature of the lamby crank allow it to flex more at tdc causing it to v the webs creating greater than normal extension and its needle roller adds xtra clearance on most available bearings

djh66
if u measure the gudgeon pin to crown height and contact richard he,ll let u know if its right
does the piston sit 3mm below transfers at bottom dead centre?

[djh66]

thats about correct Dan , wow 4.46 am sounds like u had a good night out

this is how it can be put to good use
i use the method to check wear on race motors thru the season
start with 1.2 squish with solder and 1.1mm without shows a 0.1 deflection down due to tolerances in bearings which will mean on the up stroke with extension of components will reult in a 1mm squish thats without heat expansion and rod stretch etc ,i find towards the end of the season the squish gets bigger ,too big is followed by a bearing failure
the narrow nature of the lamby crank allow it to flex more at tdc causing it to v the webs creating greater than normal extension and its needle roller adds xtra clearance on most available bearings

djh66
if u measure the gudgeon pin to crown height and contact richard he,ll let u know if its right
does the piston sit 3mm below transfers at bottom dead centre?

Darrell,
I will pm Richard, the piston sits just about right at BDC, a 'nats cock' below exhaust port. Thanks

[djh66]

A pic of barrel with no head on, fully seated.

[djh66]

Hopefully, abit clearer!

By thatnuttysound at 2012-03-25

By thatnuttysound at 2012-03-25